Offset gearboxes can be used in aircraft, as for adapting electrical power generating equipment or other accessories to the existing aircraft engines in a retrofit. Installed length, angular orientation and input speed of the accessory such as the electrical power generating equipment can be optimized by use of and offset gearbox. Offset gearboxes normally contain a lubricant, typically oil, for lubrication of the gears therein. Internal gearbox heat, created by bearings, gear meshes and pump(s) of the gearbox, must be dissipated to maintain acceptable oil operating temperatures within the gearbox. A cooling arrangement for an offset gearbox must be cost effective and not add undue weight to the aircraft.
A typical cooling circuit for an electrical power generating unit (without an offset gearbox) is shown in FIG. 1. As indicated therein, the electrical power generating unit 1, which may be an integrated drive-generator system, is drivingly connected to engine gearbox 2. A fuel/air heat exchanger 3 external to the unit 1 cools oil circulated through the heat exchanger from an oil outlet of the unit 1 by way of oil line 5. The cooled oil is returned to an oil inlet of the unit 1 by oil line 4.
A cooling arrangement for an integrated drive generator system is disclosed in U.S. Pat. No. 4,284,913. In the disclosed system of the patent, a drive unit and a generator unit of the system share a common lubricant-coolant fluid system. This system does not include an offset gearbox. See also U.S. Pat. Nos. 4,787,271; 4,844,202 and 4,447,737.